1. Field of the Invention
The present invention relates to a pressure pad device used for a magnetic tape cassette. More particularly, it relates to a pressure pad device provided with a central fulcrum structure for eliminating a clattering movement of a pad as found in the conventional pressure pad device.
2. Description of the Related Art
In general, a magnetic tape cassette is provided with a pressure pad device comprising a leaf spring and a pad which forces a magnetic tape to a magnetic recording/reproducing head. In a magnetic tape microcassette, a pad is attached to each left and right side portions of a leaf spring at a symmetrical position. This is because a magnetic head is provided at a position apart from the center of a recorder for a microcassette for the reason of requirement in design and accordingly, it is necessary to provide separately pads for the side A and side B of the microcassette. When the microcassette is set in a recorder to use the side A, one of the pads opposes the magnetic head and when it is reversed to use the side B, the other pad opposes the head. Thus, there has been used a pressure pad device constructed in such a mannger that the center of a leaf spring is supported by a supporter formed in the cassette and each pad is attached to near each end of the left and right side portions of the leaf spring at a symmetrical position with respect to the center of the leaf spring.
An example of the conventional pressure pad device will be described with reference to drawing. FIG. 1 is a plan view of a magnetic tape microcassette. A pressure pad device 1 is placed at the central portion on the front side of the microcassette and just inside a magnetic tape T running through the front side of the microcassette. The pressure pad device 1 comprises a leaf spring 2 made of a single piece of a material and pads 3, 3' attached respectively to each end portion of the leaf spring 2 at a symmetrical position with respect to the center of the spring. The leaf spring is formed by bending a flexible, thin metallic plate such as phosphor bronze so that left and right portions of the leaf spring are made symmetric with respect to its center. The pads 3, 3' are generally made of felt and are bonded to the leaf spring. When the microcassette is put in the recorder, a pad is opposed to a magnetic head H through the magnetic tape, depending on whether the side A or the side B of the microcassette is used. (The pad 3' is used in the embodiment shown in FIG. 1.) The head slightly forces the magnetic tape to bring it in press-contact with the front surface of the pad with the result that the leaf spring is slightly deflected rearwards. The magnetic tape is moved between the head and the felt pad in contact therewith and under a slightly curved condition to be subjected to a predetermined operation such as recording or reproducing.
FIG. 2 is an enlarged view of the pressure pad device shown in FIG. 1. The leaf spring 2 has a central portion having a pair of projecting pieces 4, 4' which extend along both side surfaces of a supporting member 6 formed integrally on the microcassette. By engaging the supporting member with the projecting pieces, the leaf spring 2 is supported by the supporting member 6. A center projection 5 is formed at the center of the leaf spring to contact to the supporting member 6. Both ends of the leaf spring 2 are respectively forced to supporting pins 7, 7' in a flexible manner.
FIGS. 3(a) and 3(b) respectively show a plan view and a front view of a second embodiment of the conventional pressure pad device. The pressure pad device shown in FIG. 3 is the same as that in FIG. 2 except for the central fulcrum structure. Namely, an enlarged portion 10 is formed at the center of the leaf spring 2 and the enlarged portion is engaged with each pair of protrusions 11 formed on the inner surfaces of upper and lower half casings of the microcassette whereby the leaf spring is placed in a right position.
FIGs. 4(a) and 4(b) show a third embodiment of the conventional pressure pad device. In this case, a recess 12 formed both sides of the central enlarged portion 10 of the leaf spring 2 and protrusions 13 formed on the upper and lower half casings of the microcassette are respectively fitted into the recesses 12.
Thus, the central fulcrum portion of the conventional pressure pad device as exemplified by three embodiments as described above is of a type such that one of more projections or one or more recesses are formed in the microcassette and the leaf spring, and one member is confined by inserting the projections into the recesses of the other member. In preparation of these members, it has been essentially necessary for these member to have allowances with the result that it has not been possible to eliminate a clattering movement of the leaf spring in the lateral direction. Namely, gaps P are necessarily produced between the supporting member 6 and the projecting pieces 4, 4' extending along both sides of the supporting member 6 as shown in FIG. 2. In case as shown in FIG. 3, gaps P are produced between the enlarged portion 10 of the leaf spring 2 and the protrusions 11. In the embodiment of FIG. 4, gaps P are produced between the inner sides of the recess 12 of the enlarged portion and the protrusion 13.
Presence of such gaps cause deflection in position of the pad with respect to the magnetic head and accordingly, a pad pressure is changed to thereby cause adverse affect to characteristic such as output variation, phase difference etc. Since support of the leaf spring is unstable at the central fulcrum portion, a vibration is induced in the pad during running of the magnetic tape to undesirably cause, for instance, wowflutter, creaking of the magnetic tape as well as reduction of the characteristics described above. While various improvements in magnetic materials for magnetic tapes and running characteristic of the tape as well as magnetic tapes having a high performance have been developed, stability of the function of the pad is also required.